Method and apparatus for determining the cross section of material using a sound field

ABSTRACT

Method and apparatus by which the approximate cross section of filamentary or wire form material is determined, wherein the material is passed through a sound field having standing waves of at least two different frequencies and sound pickups for detecting the frequencies so that the cross section of the material may be determined by changes in amplitude or phase of at least one of the waves. One standing wave serves to provide an indication of the cross section of the material while another standing wave adjusts the zero point of the measuring arrangement.

United States Patent A [1 91 Felix i 1451 Dec. 17, 1974 METHOD AND APPARATUS FOR DETERMINING THE CROSS SECTION OF MATERIAL USING A SOUND FIELD [75] Inventor: Ernst Felix, Uster, Switzerland [73] Assignee: Zellweger, Ltd., Ulster, Switzerland [22] Filed: Mar. 9, 1973.

[21] Appl. No.: 339,883

[30] Foreign Application Priority Data Mar. 15, 1972 Switzerland... 3828/72 [52] U.S.- Cl; 73/69 [51] Int. Cl. G01n 29/00 [58] Field of Search 73/69, 67.5 R, 67.1, 67.2, 73/67.6, 67, 159, 160; 181/.5 NP

[56] References Cited UNITED STATES PATENTS 2,538,444 1/1951 De Mars 181/5 NP 3,470,734 Ill/1969 -Agdur et ul 73/69 3,570,624 3/1971 3,75( ),46l 8/1973 Felix 73/69 FOREIGN PATENTS OR APPLICATIONS 710,124 (1/1954 Great Britain 73/69 Primary E.\'aminer--Richard C. Oueisser Aszrislant I .\'uminerStephen A. Kreitman Attorney, Agent, or FirmCraig & Antonelli 57 ABSTRACT .Method and apparatus by which the approximate cross section of filamentary or wire form material is determined, wherein the material is passed through a sound field having standing waves of at least two different frequencies and sound pickups for detecting the frequencies so that the cross section of the material may be determined by changes in amplitude or phase of at least one of the waves. One standing wave serves to provide an indication of the cross section of the material while another standing wave adjusts the zero point of the measuring arrangement.

26 Claims, 9 Drawing Figures OConnor 73/675 PATENTEL DEC 1 H974 3854,32};

SHEET 2 BF 2 METHOD AND APPARATUS FOR DETERMINING THE CROSS SECTION OF MATERIAL USING A SOUND FIELD r This invention relates to a method of and an apparatus for at least approximately determining the cross section of filamentary or wire form material, more'especially of products of the textile industry and wire manufacturing industry.

There are numerous methods and apparatus for determining the cross section of such products. For example, mechanical, photoelectric and capacitive measuring systems have been extensively used for this purpose, the specific advantages of each system being offset by certain disadvantages and shortcomings.

Acoustic measuring systems, especially those which function in the ultrasonic range, have also recently been studied in some detail. In their case, the extent to -which the time taken by sound waves to reach a sound pickup from a sound generator is influenced by intro} ducing the material whose cross section is to be determined .into the area between the pickup and the generator.. This acoustic'measuring principle has pro'ven to be basically effective and has been found to have certain advantages over other conventional measuring techniques.

Nevertheless, known acoustic measuring systems are still attended by the disadvantage'that they do not have the necessary long-term stability. Accordingly, reference systems have had to be provided in order to maintain this stability. An object of the present to obviate this disadvantage.

According .to the invention there is provided a generating a sound field having standing 'waves of at least two different frequencies, sound pickups for de-.

tecting the said frequencies and means for guiding the said material through a zone in the aforementioned sound field in which both a pressure maximum of one invention is FIG. 5 is a schematic diagram of a further development of the measuring arrangement shown in FIGS. 1 and 2; i

FIG. 6 is a schematic diagram of an arrangement for filtering out different frequencies at the transmitting end;

FIG. 7.is a schematic diagram of an arrangement for filtering out different frequencies at the receiving end;

FIG. 8 is a schematic diagram of the basic measuring arrangement of FIG. IV with modified working condi tions; and

FIG. 9 is a schematic diagram of a preferred embodimentfor the sound generator and sound pickup.

- A material 1, for example, a textile yarn, the cross section of which is-to be determined, is shown in cross section in .FIG. 1 and extends perpendicularly to a soundfield which consists of standing wavesbetween surfaces 2'and 3. These standing waves are produced by a generator l4 through loudspeakers or similar electro-acoustic transducers 10, and their intensity is measured by microphones or other electroacoustic transducers 11. The interval 20 between the surfaces 2 and 3 is .selected in such a way that, at a predetermined frequency f a standing fundamental wave 4 occurs with a pressure minimum atthe surfaces 2, and 3 and a pressure maximum'at half the distance 20. Accordingly, the pressure minirna have to meet at the surfaces 2 and 3 and a pressure maximum occurs in the middle plane between the surfaces. By introducing an object into the range of the velocity maxima or minima; the transit time is increased, i.e., the time for sound to travel the distance 20 is increased and the voltage measurable at the microphone, vl1 or its phase position undergoes a change. r

If a standing wave is produced with a frequency f5 equal to atleast twice the frequency f, a wave 5 is formed with an oscillation node midwaybetween the surfaces2 and 3. An object 1 introduced at the point of this oscillation node then shortens the transit time of the sound, so that, in this case, the change in the signal measured by the microphone 11 runs in the corresponding direction. By suitably combining the sound pressures picked up by the microphone 11 in a discriminator 15, an indicating and/or recording instrument 16 is able directly to indicate and/or record the quantity i of the test material 1 in the sound field.

frequency and also a velocity maximum of another frequency occur.

The stationary waves of these two frequencies produced by the sound generators-can becontinuously intermittently transmitted. 1 i

The invention is described in detail in FIG. I isa schematic diagram of a first basic measuring arrangement; I

FIG. 2 is a schematic diagram of another basic measuring arrangement; i

FIG. 3 is a diagram illustrating in principle an acoustic feedback oscillator;

FIG. 4 is aschematic diagram of another acoustic feedback oscillator for various frequencies;

the following" with reference to the accompanying'drawings, wherein;

At a'frequency f therefore, the 'test material 1 increases the transit time whereas, at a higher frequency f for example, the transit time is shortened. With each one of these frequencies it is possible to obtain a signal corresponding tothe cross section of the test-material and to determine the cross section from this signal. Through the combination of these signals, whether continuous or intermittent, it is possible to eliminate interference effects. If, for example, the temperature changes, the transit times of both frequencies f, and f change in the same way.'Similarly, if the distance -20 between the sound generator 10 and the pickup 11 is reduced, the transit times. are also changed in the same way. The same also occurs when the atmosphere surrounding the sound generator 10 or the pickup 11 is changed through the deposition of foreign bodies, i.e., by soiling-This is an important advantage, especially for testing products of the textile industry, where the extent to which the measuring elements of all of the systems is impaired by deposits is particularly pronounced.

The material 1 does not necessarily have to pass exactly midway between the surfaces 2 and 3. By suitably selecting the stationary wave and its oscillation nodes, i.e., through using correspondingly high frequencies in relation to the fundamental wave 4, it is possible to use other material positions. FIG. 2's hows a measuring system in which the second harmonic 6 and the fourth harmonic 7 are present between the surfaces 2 and 3, while the test material 1 is positioned at one quarter-of the distance 20 from the surface 2. In this example similar conditions would also obtain if the test material 1 were to be positioned at three quarters of the distance 20.

It is of particular advantage to combine the sound generator 10 and the sound pickup '11 into an oscillator excited in known manner by acoustic feedback, in which case the oscillator frequency is determined from the transit times between the sound generator 10 and the sound pickup 11. FIG. 3 shows a basic circuit arrangement suitable for this purpose. A signal U obtained in the sound pickup 11 passes back to the sound generator 10 through an amplifier 30. The frequency adjusted as the oscillator frequency will be that frequency for which the phase relationship required for maintaining the oscillations is given in the sound pickup 11. If no phase shift (or a phase shift through 360) occurs in the amplifier '30, a stationary wave whose wavelength corresponds to twice the distance 20 between the surfaces 2 and 3 is formed in the sound field 20. If by contrast the amplifier is designed in such a way that a phase shift of the signal U through l80 takes place in it, the frequency of a wavelength formed will exactly correspond to the distance 20.

However, two frequenciesf, andf can also be simultaneously generated. The corresponding apparatus is particularly simple because the feedback from the sound pickup 11 to the sound generator 10 can be carried out simply by sign change at both frequencies.

FIG. 4 shows a combination of a sound generator 10 and a sound pickup 11 with two parallel amplifiers 30 and 31, of which the amplifier 30 produces no phase shift while the amplifier 31 works-with a phase shift of 180. One or the other of the amplifiers can be placedin the feedback path, for example, intermittently, by a switch 32. I

In an arrangement of the kind shown in FIG.'4", however, diffuculties can arise as a result of so-called pulling effects, i.e., through the well-known phenomenon that the two oscillation systems 2,3, 30 and 2, 3, 31 do not oscillate at their true. resonance frequencies f, and f but instead they (or their harmonics) influence (pull") one another in such a way that an integral frequency ratio is formed. Although it is possible in principle satisfactorily to separate both frequencies, it can be of advantagein some cases to use at least two sound pickups. FIG. 5 shows such an arrangement with two sound pickups 11 and 13, two sound 'generators 10 and 12 also being provided for reasons of symmetry.

Different combinations are, of course, possible. For

a certain frequency f, or f It is also possible, however,

to superimpose the two frequencies in the generators. In this case, the frequency f can be directly delivered to the generators as an approximately even-numbered multiple of the fundamental frequency, while the frequency f, can be delivered as an odd-numbered multi ple of the fundamental frequency to the one generator in phase and to the other generator shifted in phase by This arrangement is shown by way of example in FIG. 6.

In an arrangement of the-kind 'shown in FIG. 7, in which one receiver is provided on either side of the sound field, it is of particular advantage to form both the sum and the difference of the signals received. Difference formation only produces signals of oddnumbered frequencies in relation to the fundamental frequency of the resonator, because the signals of the approximately even-numbered frequencies cancel one another out in-view of the identical phase position on both sides. By contrast, sum formation only produces a signal for the approximately even-numbered frequencies because the oddnumbered frequencies are eliminated. Accordingly, the difference signal corresponds to the frequency f, and the sum signal to the frequency intermittently, the apparatus shown in FIGS. 5 and 6 are, of course, unnecessary. It is possible, for example, in an apparatus of the kind shown in FIG. 1, to generate the frequency f, which is sufficient formeasuring the cross section, for a prolonged periodand only to generate the frequency f which detects the magnitude-of extraneous effects and subsequently compensates for them in a known manner, for relatively short time intervals. It can be of advantage in some cases to displace the test material 1 slightly from the true pressure maximum of the standing wave with the frequency f because slightly outside this pressure maximum there is a zonein which the test material 1 has. hardly any effect upon the transit time (during transition from the reduction to the increase in transit time). As a result, the.frequency f can be used as a zero-point value.

There is no need for the frequency ratio between f and f to amount to approximately two, as in the examples given above. Instead, solutions in which, forexample, the ratio between the frequencies is far higher, are also possible. Ratios of even to odd numbers are of particular advantage. One example is illustrated in FIG. 8.

In this case, the frequency f is four times the frequency f (curve 8)."v

The principal function in the arrangements described in the preceding examples is to .determine the cross section of the test material 1 as exactly as possible. For

certain applications, however, exact measurement of the cross section is unnecessary,and a so-called yes-no answer is sufficient, in other words, it is'only desired to know whether testmaterial is or is not present. This is necessary, for example, in monitoring a production cycle when it is merely'desired to detect whether or not test material is present. The apparatus-according to the invention is ideally suitable for purposes such as these, because it has the necessary long-term stability.

vantageously built into flat, parallel surfaces 2 and 3. However, they do not necessarily have to be active over the entire surface (FIG. 8). Neither are parallel surfaces absolutely essential. Other forms are also sufficient, providing it is-possible to obtain standing waves with at least two different wavelengths. FIG. 9 shows an embodiment in which the arrangement is such that,-for at least one harmonic, it represents a resonator in the form of an open pipe.

What is claimed is:

1. A method of at least approximately determining the cross section of filamentary or wire form material, comprising the steps of generating standing waves with at least two different frequencies within a resonator tuned such that at least one pressure maximum of thefirst standingwave and at least one pressure minimum of another standing wave'substantiallycoincide at a point in the resonator, guiding the material to be tested through said point and. detecting variations in said standing waves produced by the presence of said mateof detecting variations in the standingwaves includesfrequency is an odd-numbered multiple of this fundamental frequency, the said other frequency being delivered to one generator in phase and to the other generator in opposite phase.

14. A method as claimed in claim 1 wherein said step of detecting variations in the standing waves includes forming the sum and the difference from signals obtained by means of sound pickups from the standing waves, the sum and difference signals thus obtained 16. An apparatus as claimed in claim 15 wherein the sound generator and the sound pickup are parts of an oscillating resonance system and are connected by at determining from the first standing wave the cross section of the test material and adjusting the zero point of the measuring'arrangement on the basis of the other the step of feeding back the detected standing waves for spontaneously generating the waves in said resonator. i

6. A method. as claimed. in claim 5 whereinsaid feed ing back of the detected standing waves is performed so as to not produce any additional phase shift between the input to the resonator and the output thereof.

7. A method as claimed in claim 5 wherein said feeding back of the detected standing waves is performed so that an additional phase shift is produced between the input to the resonator and the output thereof.

8. A method as claimed in claim 5- wherein said feeding back of the detected standing waves is provided by separate parallel paths effecting feedback without phase shift and feedback with phase shift, respectively.

least one feedback path.

17. An apparatus as claimed in claim 16 wherein the sound field containing the standing waves determines the natural frequency'of the resonance system;

18. An apparatus as claimed in claim 16 wherein there isat least one amplifier in the feedback path.

19. An apparatus as claimed in claim 18 wherein an amplifier which does not produce any phase shift is arranged in one feedback path, while an amplifier which does produce a phase shift is arranged in a second feedback path.

20. An apparatus as claimed in claim 15 wherein a sound generator for generating two frequencies-and a sound pickup for detecting the said frequencies are provided.

21. An apparatus as claimed in claim 15 wherein a sound generator and a sound pickup are providedfor generating one frequency and'another sound generator and another sound pickup are provided for generating another frequency.

9. A method as claimed in claim 8 wherein the respective parallel feedback paths are alternately switched on and off.

10. A method as claimed in claim 1 wherein the ratio between the frequencies is at least approximately integral.

ll. A method as claimed in claim 10 wherein the. a

22. An apparatus as claimed in claim 21 wherein the sound generators and the sound pickups are arranged one on either side of the sound field.

23. An apparatus as claimed in claim 22 wherein one sound generator and the corresponding sound pickup are arranged offset in relation to the other sound generator and sound pickup.

24. An apparatus as claimed in claim 15 wherein the sound generator and the sound pickup are in the form of an open pipe.

25. An apparatus as claimed in claim 15 wherein the tor in opposite phase.

multiple of a fundamental frequency while the other 26. An apparatus as claimed in claim 15 comprising means for obtaining the sum and difference of the signals obtained from two sound pickups, the sums and differences thus formed being coupled back to at least one sound generator. 

1. A method of at least approximately determining the cross section of filamentary or wire form material, comprising the steps of generating standing waves with at least two different frequencies within a resonator tuned such that at least one pressure maximum of the first standing wave and at least one pressure minimum of another standing wave substantially coincide at a point in the resonator, guiding the material to be tested through said point and detecting variations in said standing waves produced by the presence of said material to be tested.
 2. A method as claimed in claim 1 wherein the standing waves are continuously and simultaneously generated.
 3. A method as claimed in claim 1 wherein the standiNg waves of different frequencies are produced intermittently in succession.
 4. A method as claimed in claim 1 wherein said step of detecting variations in the standing waves includes determining from the first standing wave the cross section of the test material and adjusting the zero point of the measuring arrangement on the basis of the other standing wave.
 5. A method as claimed in claim 1, further including the step of feeding back the detected standing waves for spontaneously generating the waves in said resonator.
 6. A method as claimed in claim 5 wherein said feeding back of the detected standing waves is performed so as to not produce any additional phase shift between the input to the resonator and the output thereof.
 7. A method as claimed in claim 5 wherein said feeding back of the detected standing waves is performed so that an additional phase shift is produced between the input to the resonator and the output thereof.
 8. A method as claimed in claim 5 wherein said feeding back of the detected standing waves is provided by separate parallel paths effecting feedback without phase shift and feedback with phase shift, respectively.
 9. A method as claimed in claim 8 wherein the respective parallel feedback paths are alternately switched on and off.
 10. A method as claimed in claim 1 wherein the ratio between the frequencies is at least approximately integral.
 11. A method as claimed in claim 10 wherein the ratio of the frequencies is substantially that of an even to an odd integer.
 12. A method as claimed in claim 1 wherein the standing waves of at least the higher frequencies are formed in a pair of resonators acting as open pipes.
 13. A method as claimed in claim 1 wherein the frequencies are superimposed in two sound generators, one frequency being an approximately even-numbered multiple of a fundamental frequency while the other frequency is an odd-numbered multiple of this fundamental frequency, the said other frequency being delivered to one generator in phase and to the other generator in opposite phase.
 14. A method as claimed in claim 1 wherein said step of detecting variations in the standing waves includes forming the sum and the difference from signals obtained by means of sound pickups from the standing waves, the sum and difference signals thus obtained each being returned to a respective sound generator.
 15. An apparatus for at least approximately determining the cross section of filamentary or wire form material comprising means for generating a sound field having standing waves of at least two different frequencies, sound pickup means disposed in spaced relationship to said sound generating means for detecting the said frequencies and means for guiding the said material through a zone in the aforementioned sound field at a point in which both a pressure maximum of one frequency and a velocity maximum of another frequency occur.
 16. An apparatus as claimed in claim 15 wherein the sound generator and the sound pickup are parts of an oscillating resonance system and are connected by at least one feedback path.
 17. An apparatus as claimed in claim 16 wherein the sound field containing the standing waves determines the natural frequency of the resonance system.
 18. An apparatus as claimed in claim 16 wherein there is at least one amplifier in the feedback path.
 19. An apparatus as claimed in claim 18 wherein an amplifier which does not produce any phase shift is arranged in one feedback path, while an amplifier which does produce a phase shift is arranged in a second feedback path.
 20. An apparatus as claimed in claim 15 wherein a sound generator for generating two frequencies and a sound pickup for detecting the said frequencies are provided.
 21. An apparatus as claimed in claim 15 wherein a sound generator and a sound pickup are provided for generating one frequency and another sound generator and another sound pickup are provided for generating another frequency.
 22. An apparatus as claiMed in claim 21 wherein the sound generators and the sound pickups are arranged one on either side of the sound field.
 23. An apparatus as claimed in claim 22 wherein one sound generator and the corresponding sound pickup are arranged offset in relation to the other sound generator and sound pickup.
 24. An apparatus as claimed in claim 15 wherein the sound generator and the sound pickup are in the form of an open pipe.
 25. An apparatus as claimed in claim 15 wherein the frequencies are derived from a fundamental frequency, one of the derived frequencies being an odd-numbered multiple and the other frequency an approximately even-numbered multiple of this fundamental frequency, one of the frequencies being applied to one sound generator in phase and to another sound generator in opposite phase.
 26. An apparatus as claimed in claim 15 comprising means for obtaining the sum and difference of the signals obtained from two sound pickups, the sums and differences thus formed being coupled back to at least one sound generator. 